1. Field of the Invention
The present invention pertains to the art of washing machines, such as clothes washing or dish washing machines and, more particularly, to an automatic washing machine incorporating a system for controlling the temperature of washing liquid introduced into a tub or basket of the machine during an operating cycle.
2. Discussion of the Prior Art
Essentially every washing machine has some type of control to set the temperature of the fill water entering an associated washing machine tub. Typically, systems known in the art rely on controlling the amount of fill water supplied through hot and cold water valves to establish a desired temperature. More specifically the desired temperature in such a known system is established by opening one or both of the controlling hot and cold water valves. For instance, hot water would be supplied by opening the hot water valve and closing the cold water valve; warm water would be supplied with both valves open; and cold water would be supplied by opening the cold water valve while leaving the hot water valve closed. This basic type of system may not be considered satisfactory for many reasons, mainly due to the potential for varying temperatures and pressures of the incoming cold and hot water streams. Therefore, such a simple system can result in widely ranging temperatures of the fill water supplied to the washing tub between different washing operations.
Water temperature is an important factor in cleaning. For example, in a clothes washer, if the wash water temperature is too cold for a given operation, inadequate soil removal can result, while a wash temperature which is too hot can result in clothing damage, as well as a waste of energy. In fact, it has been noted that certain detergents work well within a relatively narrow temperature range such that fill water outside a desired temperature range can degrade the performance of a detergent.
In an attempt to address this problem, many proposals have been set forth. Mostly, these solutions involve providing complicated control systems to control the flow of fill water provided by the hot and cold water valves. Typically, these systems incorporate one or more temperature sensors which provide feedback signals used to more precisely control the water valves. However, these temperature sensors are both extremely costly and prone to failure such that these overall systems raise economic and reliability concerns.
For example, U.S. Pat. No. 4,528,709 proposes a washing machine temperature control system wherein the temperature and flow rate of hot and cold water inlets are separately sensed. The system calculates from this data the quantity of hot and cold water necessary to arrive at a desired overall temperature given a selected amount of water desired in the washing tub. Of course, such a system requires at least two thermistor type sensors and a flow meter or the equivalent in order to obtain the necessary data. As stated above, such sensors are both expensive and prone to failure.
U.S. Pat. No. 4,330,081 proposes a water temperature control system for a clothes washing machine that is designated to control a desired water temperature for use in the clothes washing tub. This system essentially obtains the desired temperature values by memorizing desired temperatures based on the type of clothes to be washed, such as cotton, wool, polyester, etc. Once again, in order to achieve the desired results, the temperature of the combined water flow must be sensed, such as through the use of a thermistor. In addition, in accordance with this patented arrangement, a multi-vibrator is coupled to input gates of a microprocessor. Once again, this solution suffers from the defect of employing thermistors which are both expensive and prone to failure, as well as a suspect multi-vibrator arrangement.
As a final example, U.S. Pat. No. 5,439,019 discloses a method and apparatus for filling a washing tub of an automatic clothes washer that is designed to actively regulate the temperature of the final volume of water present in the washing tub based on a preselected temperature inputted by an operator of the washing machine. Once again, this patent discloses the use of a thermistor to achieve the temperature control function. Specifically a thermistor is used to obtain a measurement which is representative of the water flowing through a mixing valve.
Based on the above, there exists a need in the art of automatic washing machines for an adjustable water control system which can accurately control the temperature of the fill water entering the washing tub while not requiring the use of expensive temperature sensors and their associated electronics.